The MAPKs regulate cell growth, differentiation, and stress responses, and many critical signaling pathways are subject to cross-regulation by MARK signaling. Previous studies have yielded evidence of crosstalk between the MARK pathways and androgen receptor (AR) signaling, which plays a critical role in growth control of both normal prostate and prostate cancer. We have shown that the MAPK-like protein, Nemo-like kinase (NLK) expression is altered during prostate cancer progression, and that NLK dramatically inhibits AR-mediated signaling and ultimately stimulating apoptosis in CaP cells. The goal of this project is to elucidate the mechanisms of NLK effects on AR signaling in prostate cells and to evaluate its promise as a new therapeutic target. We will perform mechanistic studies on interaction of NLK with AR, including transcriptional analysis and protein-level modifications, and cofactors associations. We will also investigate the proapoptotic effects of NLK in prostate cells and its relation to inhibition of AR signaling, and study in vivo effects of NLK using our advanced animal models. A deeper understanding of the NLK roles in prostate cancer progression and regulation of AR-directed transcription and its biological effects will lead to an appreciation of the value of reconstituting functional NLK signaling in CaP and point the way to new modes of therapeutic intervention in this disease. The specific aims of this proposal are intended to elucidate the nature and mechanisms of induction of apoptosis in CaP cells by NLK and characterize the effects of NLK expression on critical signaling pathways in these cells. Specific aims: 1) To investigate associations of NLK expression with clinical parameters of prostate cancer. 2) To investigate the mechanisms of NLK effects on AR-directed transcription. 3) To investigate the mechanisms whereby NLK promotes apoptosis of CaP cells. 4) To investigate the effects of NLK expression on prostate cancer tumors in vivo. Health relevance: Advanced prostate cancer is a devastating, fatal, and almost untreatable disease. By studying the ability of nemo-like kinase to kill even prostate-cancer cells that are resistant to other treatments, we hope to point the way to new and promising therapeutic approaches for advanced prostate cancer.